Sintered ferrite magnet and motor provided therewith

ABSTRACT

Provided is a sintered ferrite magnet  10  that comprises Sr ferrite having a hexagonal crystal structure, wherein the total amount of Na and K is 0.004 to 0.31% by mass in terms of Na 2 O and K 2 O, an amount of Si is 0.3 to 0.94% by mass in terms of SiO 2 , and the following Expression (1) is satisfied.
 
1.3≦(Sr F +Ba+Ca+2Na+2K)/Si≦5.7  (1)
 
     [In Expression (1), Sr F  represents an amount of Sr, on a molar basis, other than Sr which constitutes the Sr ferrite, and Ba, Ca, Na, and K represent amounts of respective elements on a molar basis.]

TECHNICAL FIELD

The present invention relates to a sintered ferrite magnet and a motorprovided therewith.

BACKGROUND ART

As magnetic materials that are used in a sintered ferrite magnet, Baferrite, Sr ferrite, and Ca ferrite which have a hexagonal crystalstructure are known. Recently, among these magnetic materials, as amagnet material for motors and the like, magnetoplumbite type (M type)Sr ferrite has been mainly employed. The M type ferrite is expressed by,for example, General Formula of AFe₁₂O₁₉. The Sr ferrite has Sr at an Asite of the crystal structure.

To improve magnetic characteristics of the sintered ferrite magnet,improvement in the magnetic characteristic is attempted by substitutingparts of an A-site element and a B-site element with a rare-earthelement such as La, and Co, respectively. For example, Patent Literature1 discloses a technology of improving a residual magnetic flux density(Br) and a coercive force (HcJ) by substituting parts of the A site andthe B site with a specific amount of rare-earth element and Co.

As a representative use of the sintered ferrite magnet, a motor may beexemplified. The sintered ferrite magnet that is used in a motor isdemanded to be excellent in both characteristics of the Br and the HcJ.However, generally, it is known that the Br and the HcJ are in atrade-off relationship. Therefore, it has been demanded to establish atechnology capable of further improving both characteristics of Br andHcJ.

As an index representing magnetic characteristics in consideration ofboth characteristics of Br and HcJ, a calculation expression of Br(kG)+⅓HcJ (kOe) is known (for example, refer to Patent Literature 1). Asthis value is high, it can be said that the sintered ferrite magnet issuitable for a use such as a motor in which high magneticcharacteristics are demanded.

CITATION LIST Patent Literature

-   [Patent Literature 1] Japanese Unexamined Patent Application    Publication No. 11-154604

SUMMARY OF INVENTION Technical Problem

As described in Patent Literature 1, it is effective to improve themagnetic characteristics by controlling a composition of main crystalgrains that constitutes the sintered ferrite magnet. However, it isdifficult to greatly improve the magnetic characteristics of thesintered ferrite magnet in the related art by controlling only thecomposition of crystal grains. On the other hand, some accessorycomponents that are contained in the sintered ferrite magnet have anoperation of improving the magnetic characteristics or sinterability.However, reliability in excellent strength, external appearance, and thelike of the sintered ferrite magnet may be damaged depending on a kindof the accessory component or an amount thereof in some cases. Forexample, when using a sintered ferrite magnet having low strength or asintered ferrite magnet in which foreign matter tends to precipitate ona surface thereof in a motor, there is a concern that the sinteredferrite magnet is broken, or peeled off and falls down during use of themotor. Therefore, a sintered ferrite magnet, which has not only themagnetic characteristics and but also high reliability, has beendemanded.

The invention has been made in consideration of the above-describedcircumstances, and an object thereof is to provide a sintered ferritemagnet which is excellent in both characteristics of a residual magneticflux density (Br) and a coercive force (HcJ), and which has highreliability. In addition, another object of the invention is to providea motor which has high efficiency and which is excellent in reliability.

Solution to Problem

The present inventors have made an examination on improvement ofmagnetic characteristics by giving attention to the entire compositionof the sintered ferrite magnet and a composition of a grain boundary inaddition to a composition of a crystal grain. As a result, the presentinventors have found that when a predetermined accessory component iscontained, the magnetic characteristics and the reliability of thesintered ferrite magnet can be improved, and they have accomplished theinvention.

That is, according to an aspect of the invention, there is provided asintered ferrite magnet comprising Sr ferrite having a hexagonal crystalstructure, wherein a total amount of Na and K is 0.004 to 0.31% by massin terms of Na₂O and K₂O, an amount of Si is 0.3 to 0.94% by mass interms of SiO₂, and the following Expression (1) is satisfied.1.3≦(Sr_(F)+Ba+Ca+2Na+2K)/Si≦5.7  (1)

Here, in Expression (1), Sr_(F) represents an amount of Sr, on a molarbasis, other than Sr which constitutes the Sr ferrite, and Ba, Ca, Na,and K represent amounts of respective elements on a molar basis.

The sintered ferrite magnet of the invention is excellent in bothcharacteristics of Br and HcJ and has high reliability. Although notapparent, the present inventors consider that the reason of obtainingthese effects is because a grain boundary composition of the sinteredferrite magnet contributes to the effects. That is, it is consideredthat silicate glass, which contains Sr other than Sr that constitutesthe Sr ferrite and at least one of Ba, Ca, Na, and K as a constituentelement, is formed at the grain boundary of the sintered ferrite magnet.It is considered that the sintered ferrite magnet of the invention has agrain boundary composition in a ratio with which the silicate glass isstably formed. Accordingly, the sintered ferrite magnet tends to have astable and dense structure, and thus it is considered that the sinteredferrite magnet has high Br and HcJ and high reliability.

In addition, it is preferable that the sintered ferrite magnet of theinvention satisfy the following Expression (2). According to this, it ispossible to further increase the value of Br+⅓HcJ. In addition, inExpression (2), Sr_(F) represents an amount of Sr, on a molar basis,other than Sr which constitutes the Sr ferrite, and Ba, Ca, Na, and Krepresent amounts of respective elements on a molar basis.1.7≦(Sr_(F)+Ba+Ca+2Na+2K)/Si≦23  (2)

In addition, it is preferable that the sintered ferrite magnet of theinvention satisfy the following Expression (3). According to this, thesintered ferrite magnet has more excellent magnetic characteristics.Br+⅓HcJ≧5.3  (3)

In Expression (3), Br and HcJ represent a residual magnetic flux density(kG) and a coercive force (kOe), respectively.

In the sintered ferrite magnet of the invention, it is preferable thatan average grain size of crystal grains of the Sr ferrite be 1.0 μm orless, and a ratio of crystal grains, which have a grain size of 2.0 μmor more, on the number basis be 1% or less. According to this, it ispossible to make the magnetic characteristics and the reliability behighly compatible with each other.

According to another aspect of the invention, there is provided a motorincluding the above-described sintered ferrite magnet. The motorincludes the sintered ferrite magnet having the above-describedcharacteristics, and thus the motor has both of high efficiency and highreliability.

Advantageous Effects of Invention

According to the invention, it is possible to provide a sintered ferritemagnet which is excellent in both characteristics of Br and HcJ andwhich has high reliability. In addition, it is possible to provide amotor which has high efficiency and which is excellent in reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically illustrating a preferredembodiment of a sintered ferrite magnet of the invention.

FIG. 2 is a graph obtained by plotting a relationship between Br (G) andHcJ (Oe) of a plurality of sintered ferrite magnets in Examples andComparative Examples of the invention.

FIG. 3 is an electron microscope photograph illustrating an enlargedcross-section of a sintered ferrite magnet of Example 73 (magnification:10,000 times).

FIG. 4 is an electron microscope photograph illustrating an enlargedcross-section of a sintered ferrite magnet of Example 74 (magnification:10,000 times).

FIG. 5 is an electron microscope photograph illustrating an enlargedcross-section of a sintered ferrite magnet of Comparative Example 14(magnification: 10,000 times).

FIG. 6 is a graph illustrating a grain size distribution of crystalgrains of Sr ferrite that is contained in the sintered ferrite magnet ofExample 73.

FIG. 7 is a graph illustrating a grain size distribution of crystalgrains of Sr ferrite that is contained in the sintered ferrite magnet ofExample 74.

FIG. 8 is a graph illustrating a grain size distribution of crystalgrains of Sr ferrite that is contained in the sintered ferrite magnet ofComparative Example 14.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferred embodiment of invention will be described indetail with reference to the attached drawings as necessary.

FIG. 1 is a perspective view schematically illustrating a sinteredferrite magnet of this embodiment. The sintered ferrite magnet 10 has acurved shape in which an end face has an arc shape, and generally, thesintered ferrite magnet 10 has a shape called an arc segment shape, a Cshape, a roof tile shape, or a bow shape. For example, the sinteredferrite magnet 10 is suitably used as a magnet for motors.

The sintered ferrite magnet 10 is a sintered Sr ferrite magnet thatcontains M-type Sr ferrite having a hexagonal structure as a maincomponent. For example, the Sr ferrite that is a main component isexpressed by the following Formula (4).SrFe₁₂O₁₉  (4)

In the Sr ferrite of Expression (4), parts of A-site Sr and B-site Femay be substituted with an impurity or an intentionally added element.In addition, a ratio between the A site and the B site may slightlydeviate. In this case, the Sr ferrite may be expressed, for example, bythe following General Formula (5).R_(x)Sr_(1-x)(Fe_(12-y)M_(y))_(z)O₁₉  (5)

In Formula (5), for example, x and y range from 0.1 to 0.5, and z rangesfrom 0.7 to 1.2.

For example, M in General Formula (5) represents one or more kinds ofelements selected from the group consisting of Co (cobalt), Zn (zinc),Ni (nickel), Mn (manganese), Al (aluminum), and Cr (chromium). Inaddition, for example, R in General Formula (5) is a rare-earth elementand represents one or more kinds of elements selected from the groupconsisting of La (lanthanum), Ce (cerium), Pr (praseodymium), Nd(neodymium), and Sm (samarium). In addition, in this case, Sr_(F) can becalculated on the assumption that M and R constitute the Sr ferrite asexpressed by General Formula (5).

A mass ratio of the Sr ferrite in the sintered ferrite magnet 10 ispreferably 90% by mass or more, more preferably 95% by mass or more, andstill more preferably 97% by mass or more. As described above, it ispossible to further improve the magnetic characteristics by reducing themass ratio of a crystal phase different from the Sr ferrite.

As an accessory component, the sintered ferrite magnet 10 contains acomponent different from the Sr ferrite. Examples of the accessorycomponent include oxides. Examples of the oxides include oxides andcomposite oxides which have at least one kind of elements selected fromthe group consisting of K (potassium), Na (sodium), Si (silicon), Ca(calcium), Sr (strontium), and Ba (barium) as a constituent element.Examples of the oxides include SiO₂, K₂O, Na₂O, CaO, SrO, and BaO. Inaddition, silicate glass may be contained.

The total amount of Na and K in the sintered ferrite magnet 10 is 0.004to 0.31% by mass in terms of Na₂O and K₂O. The lower limit of the totalamount of Na and K is preferably 0.01% by mass in terms of Na₂O and K₂O,more preferably 0.02% by mass, and still more preferably 0.03% by mass.When the total amount of Na and K excessively decreases, a sinteringtemperature cannot be lowered, and thus there is a tendency that graingrowth of crystal grains occurs and thus it is difficult to obtainsufficiently high magnetic characteristics.

The upper limit of the total amount of Na and K is preferably 0.2% bymass in terms of Na₂O and K₂O, more preferably 0.15% by mass, and stillmore preferably 0.1% by mass. When the total amount of Na and Kexcessively increases, a white powder tends to be generated on a surfaceof the sintered ferrite magnet 10. When the powder is generated on thesurface of the sintered ferrite magnet 10, for example, adhesion betweena motor member and the sintered ferrite magnet 10 decreases, and thusthere is a possibility that the sintered ferrite magnet 10 may be peeledfrom the motor member. That is, the reliability of the sintered ferritemagnet 10 deteriorates.

An amount of Si in the sintered ferrite magnet 10 is 0.3 to 0.94% bymass in terms of SiO₂. The lower limit of the amount of Si is 0.4% bymass in terms of SiO₂, and more preferably 0.45% by mass. When theamount of Si excessively decreases, a sintered body is not sufficientlydensified, and thus the excellent magnetic characteristics tend todeteriorate. The upper limit of the amount of Si is preferably 0.9% bymass in terms of SiO₂, and more preferably 0.8% by mass. When the amountof Si excessively increases, the sufficiently excellent magneticcharacteristics tend to deteriorate.

An amount of Sr in the sintered ferrite magnet 10 is preferably 10 to13% by mass in terms of SrO from the viewpoint of further improving themagnetic characteristics and the reliability, and more preferably 10.3to 11.9% by mass. In addition, an amount of Ba in the sintered ferritemagnet 10 is preferably 0.01 to 2.0% by mass in terms of BaO from thesame viewpoint, and more preferably 0.01 to 0.2% by mass.

An amount of Ca in the sintered ferrite magnet 10 is preferably 0.05 to2% by mass in terms of CaO from the viewpoint of further improving themagnetic characteristics and the reliability, and more preferably 0.1 to1.5% by mass. In addition to these components, impurities that arecontained in a raw material, or unavoidable components that are derivedfrom a manufacturing facility may be contained in the sintered ferritemagnet 10. Examples of the impurities and the unavoidable componentsinclude oxides of Ti (titanium), Cr (chromium), Mn (manganese), Mo(molybdenum), V (vanadium), Al (aluminum), and the like.

The accessory component is mainly contained in a grain boundary ofcrystal grains of the Sr ferrite in the sintered ferrite magnet 10. Whena ratio of respective elements that are included in the accessorycomponent varies, a composition of a grain boundary varies. As a result,this variation may have an effect on the magnetic characteristics andthe reliability of the sintered ferrite magnet 10. When a ratio of aspecific element that is included in the accessory component is adjustedin a predetermined range, the sintered ferrite magnet 10 of thisembodiment has excellent magnetic characteristics and the highreliability. In addition, the amount of respective components of thesintered ferrite magnet 10 can be measured by fluorescent X-ray analysisand inductively coupled plasma emission spectroscopic analysis (ICPanalysis).

From the viewpoint of further improving the magnetic characteristics andthe reliability, the sintered ferrite magnet 10 satisfies the followingExpression (1), preferably the following Expression (1)′, still morepreferably the following Expression (6), and still more preferably thefollowing Expression (2).1.3≦(Sr_(F)+Ba+Ca+2Na+2K)/Si≦5.7  (1)1.3≦(Sr_(F)+Ba+Ca+2Na+2K)/Si≦3.2  (1)′1.3≦(Sr_(F)+Ba+Ca+2Na+2K)/Si<2.9  (6)1.7≦(Sr_(F)+Ba+Ca+2Na+2K)/Si≦2.7  (2)

In Expression (1), Expression (1)′, Expression (6), and Expression (2),Sr_(F) represents an amount of Sr, on a molar basis, other than Sr whichconstitutes the Sr ferrite, and Ba, Ca, Na, and K represent amounts ofrespective elements on a molar basis. Sr_(F) is created in a case wherea ratio of a Sr source to an Fe source is made to be more than astoichiometric ratio of the Sr ferrite [SrFe₁₂O₁₉ orR_(x)Sr_(1-x)(Fe_(12-y)M_(y))_(z)O₁₉] during a process of manufacturingthe sintered ferrite magnet 10. In a case where the amount of Sr is lessthan the stoichiometric ratio of the Sr ferrite [SrFe₁₂O₁₉ orR_(x)Sr_(1-x)(Fe_(12-y)M_(y))_(z)O₁₉], the Sr_(F) becomes a numericalvalue less than 0, that is, a negative numerical value. In this case, itis also preferable to satisfy Expression (1), Expression (1)′,Expression (6), or Expression (2).

It is considered that silicate glass containing the element, which isexemplified as an accessory component, as a constituent element isgenerated at a grain boundary of the sintered ferrite magnet 10. It isconsidered that when the sintered ferrite magnet 10 satisfies Expression(1), Expression (1)′, Expression (6), or Expression (2), a compositionof the grain boundary is stabilized, and this stabilization contributesto improvement in the magnetic characteristics and the reliability.

An average grain size of crystal grains of the Sr ferrite in thesintered ferrite magnet 10 is preferably 2.0 μm or less, more preferably1.0 μm or less, and still more preferably 0.3 μm to 1.0 μm. When theaverage grain size of crystal grains of the Sr ferrite exceeds 2.0 μm,there is a tendency that it is difficult to obtain sufficientlyexcellent magnetic characteristics. On the other hand, it is difficultto manufacture a sintered ferrite magnet in which the average grain sizeof crystal grains of the Sr ferrite is less than 0.3 μm,

The average grain size of crystal grains of the Sr ferrite of thesintered ferrite magnet 10 can be measured by using a SEM or a TEM. In acase of performing the measurement by the SEM, a cross-section of thesintered ferrite magnet is mirror-polished, and the cross-section isetched with an acid such as hydrofluoric acid. Then, the resultantetched surface is observed with the SEM. In a SEM or TEM observationimage including several hundreds of crystal grains, a contour of crystalgrains is made to be clear, and image processing and the like areperformed. Then, a grain size distribution of a c-plane is measured.“Grain size” in this specification represents the major axis (diameterin an a-axis direction) in an a-plane. The major axis is obtained as thelongest side of a “rectangle with the smallest area” which circumscribeseach of the crystal grains. In addition, a ratio of the longest side tothe shortest side in the “rectangular with the smallest area” is an“aspect ratio”. In addition, a so-called thermal etching in which asample is heated and etched may be performed instead of the etching withthe acid.

From the measured grain size distribution on the number basis, anaverage value of the grain size of crystal grains on the number basis iscalculated. In addition, a standard deviation is calculated from thegrain size distribution and the average value which are measured. Inthis specification, the average value and the grain size distributionare set as an average grain size of crystal grains of the Sr ferrite anda standard deviation thereof. It is preferable that a ratio of crystalgrains having a grain size of 2.0 μm or more to the entirety of crystalgrains of the Sr ferrite on the number basis be 1% or less, and morepreferably 0.9% or less. According to this, it is possible to obtain asintered ferrite magnet having sufficiently high magneticcharacteristics. From the same viewpoint, it is preferable that a numberaverage value (average aspect ratio) of the aspect ratio of respectivecrystal grains be approximately 1.0.

It is preferable that the sintered ferrite magnet 10 satisfy thefollowing Expression (3). Crystal grains of the Sr ferrite in thesintered ferrite magnet of this embodiment are sufficiently fine and thesintered ferrite magnet has a specific composition, and thus highmagnetic characteristics which satisfy Expression (3) are obtained. Asintered ferrite magnet, which satisfies Expression (3), hassufficiently excellent magnetic characteristics. It is possible toprovide a motor having further higher efficiency with such a sinteredferrite magnet.Br+⅓HcJ≧5.3  (3)In Expression (3), Br and HcJ represent a residual magnetic flux density(kG) and a coercive force (kOe), respectively.

FIG. 2 is a graph obtained by plotting a relationship between Br (G) andHcJ (Oe) of a plurality of sintered ferrite magnets in Examples andComparative Examples of the invention. In FIG. 2, only data satisfying arelationship of Hk/HcJ>90% is plotted. As can be seen from FIG. 2, in asintered ferrite magnet, magnetic characteristics such as Br and HcJtypically vary due to a change in manufacturing conditions such as acomposition, addition conditions, and a firing temperature. In addition,the Br and the HcJ are in a trade-off relationship. In addition, the Brand the HcJ vary in accordance with a predetermined gradient (Br+⅓HcJ).It is preferable that the sintered ferrite magnet 10 have magneticcharacteristics (Br, HcJ) on a straight line 1 (Br+⅓HcJ=5.3) in FIG. 2or an upper and right side of the straight line 1.

For example, the sintered ferrite magnet 10 may be used as a magnet ofmotors for vehicles such as motors for a fuel pump, a power window, ananti-lock brake system (ABS), a fan, a wiper, power steering, an activesuspension, a starter, a door lock, and an electric mirror. In addition,the sintered ferrite magnet 10 may also be used as a magnet of motorsfor OA/AV apparatuses such as motors for an FDD spindle, a VTR capstan,a VTR rotary head, a VTR reel, VTR loading, a VTR camera capstan, a VTRcamera rotary head, VTR camera zooming, VTR camera focusing, a radiocassette recorder capstan, a CD/DVD/MD spindle, CD/DVD/MD loading, andCD/DVD optical pickup. Furthermore, the sintered ferrite magnet 10 mayalso be used as a magnet of motors for household electrical appliancessuch as motors for a compressor of an air-conditioner, a compressor of afreezer, electric tool driving, a drier fan, shaver driving, and anelectric toothbrush. Furthermore, the sintered ferrite magnet 10 mayalso be used as a magnet of motors for FA apparatuses such as motors fordriving of a robot shaft and a joint, main driving of a robot, drivingof a machine tool table, and driving of a machine tool belt.

The sintered ferrite magnet 10 is bonded to the above-described motormember and is provided inside the motor. In the sintered ferrite magnet10 having excellent magnetic characteristics, generation of a crack andgeneration of foreign matter (white powder) on a surface aresufficiently suppressed, and thus the sintered ferrite magnet 10 isbonded to the motor member in a sufficiently strong manner. As describedabove, it is possible to sufficiently suppress the sintered ferritemagnet 10 from being peeled from the motor member. Accordingly, variousmotors provided with the sintered ferrite magnet 10 have both of highefficiency and high reliability.

The use of the sintered ferrite magnet 10 is not limited to the motors,and the sintered ferrite magnet 10 may be used, for example, as a membersuch as a generator for motorcycles, a magnet for speakers andheadphones, a magnetron tube, a magnetic field generating apparatus foran MRI, a clamper for a CD-ROM, a sensor for a distributor, a sensor foran ABS, a fuel and oil level sensor, a magnet latch, and an isolator. Inaddition, the sintered ferrite magnet 10 may be used as a target(pellet) during formation of a magnetic layer of a magnetic recordingmedium by a deposition method, a sputtering method, and the like.

Next, a method of manufacturing the sintered ferrite magnet 10 will bedescribed. The method of manufacturing the sintered ferrite magnet 10includes a blending process, a calcination process, a pulverizationprocess, a molding process in a magnetic field, and a firing process.Hereinafter, details of the respective processes will be described.

The blending process is a process of preparing a mixed powder forcalcination. In the blending process, first, starting raw materials areweighed and are blended in a predetermined ratio, and then are mixedwith a wet-type attritor, a ball mill, and the like for 1 hour to 20hours. Pulverization is also performed during the mixing. As thestarting raw materials, compounds having constituent elements of the Srferrite that is a main component are prepared.

In the blending process, powders such as SiO₂, CaCO₃, Na₂CO₃, and K₂CO₃which are accessory components may be added. As a compound that has aconstituent element of Na or K, a silicate or an organic compound(dispersing agent) that contains Na or K may be used in addition to acarbonate.

As the compounds that have the constituent elements of the Sr ferrite,compounds such as oxides, and carbonates, hydroxides, and nitrites whichbecome oxides by firing may be used. Examples of the compounds includeSrCO₃, La(OH)₃, Fe₂O₃, Co₃O₄, and the like. An average particle size ofthe starting raw material is not particularly limited. For example, theaverage particle size is 0.1 μm to 2.0 μm. It is not necessary to mixall of the starting raw materials in the blending process before thecalcination, and parts of the respective compound or the entiretythereof may be added after the calcination.

The calcination process is a process of calcinating the raw materialcomposition that is obtained in the blending process. The calcinationcan be performed in an oxidizing atmosphere such as in the air. Acalcination temperature is preferably 800° C. to 1450° C., morepreferably 850° C. to 1300° C., and still more preferably 900° C. to1200° C. A calcination time at the calcination temperature is preferably1 second to 10 hours, and more preferably 1 minute to 3 hours. An amountof the Sr ferrite in a calcined material that can be obtained by thecalcination is preferably 70% by mass or more, and more preferably 90%by mass or more. A primary particle size of the calcined material ispreferably 10 μm or less, and more preferably 2.0 μm or less.

The pulverization process is a process of pulverizing the calcinedmaterial to obtain a powder of a ferrite magnet. The pulverizationprocess may be performed in a single step, or in two steps divided intoa rough pulverization process and a fine pulverization process.Typically, the calcined material is present in a granular shape or anagglomerated shape and thus it is preferable to perform the roughpulverization process at first. In the rough pulverization process,pulverization is performed in a dry type by using a vibration rod milland the like to prepare a pulverized powder having an average particlesize of 0.5 μm to 5.0 μm. The pulverized powder that is prepared in thismanner is wet-pulverized by using a wet-type attritor, a ball mill, ajet mill, and the like to obtain a fine powder having an averageparticle size of 0.08 μm to 2.0 μm, more preferably 0.1 μm to 1.0 μm,and still more preferably 0.2 μm to 0.8 μm.

A specific surface area of the fine powder in accordance with a BETmethod is preferably 5 m²/g to 14 m²/g, and more preferably 7 m²/g to 12m²/g. For example, in a case of using the wet-type attritor, apulverization time is 30 minutes to 10 hours, and in a case of using theball mill, the pulverization time is 5 hours to 50 hours. It ispreferable that the pulverization time be appropriately adjusted inaccordance with a pulverization method.

In the pulverization process, powders such as CaCO₃, SrCO₃, and BaCO₃may be added in addition to powders such as SiO₂, Na₂CO₃, and K₂CO₃which are accessory components. As a compound that has a constituentelement of Na or K, a silicate or an organic compound (dispersing agent)that contains Na or K may be used in addition to a carbonate. Whenadding the accessory components, it is possible to improve sinterabilityand magnetic characteristics. In a case of performing wet molding, theaccessory components may flow out together with a solvent of slurry, andthus it is preferable to blend the accessory component in an amount morethan a target amount in a sintered ferrite magnet.

To increase a magnetic orientation degree of the sintered ferritemagnet, it is preferable to add polyhydric alcohol in the finepulverization process in addition to the above-described accessorycomponent. An added amount of the polyhydric alcohol is 0.05 to 5.0% bymass with respect to materials to be added, preferably 0.1 to 3.0% bymass, and more preferably 0.3 to 2.0% by mass. In addition, the addedpolyhydric alcohol is removed by thermal decomposition in the firingprocess after the molding process in a magnetic field.

The molding process in a magnetic field is a process of molding the finepowder, which is obtained in the pulverization process, in a magneticfield to prepare a molded body. The molding process in a magnetic fieldmay be performed by either dry molding or wet molding. However, the wetmolding is preferable from the viewpoint of increasing the magneticorientation degree. In a case of performing the wet molding, the slurry,which is obtained by performing the fine pulverization process in a wetmanner, may be adjusted to have a predetermined concentration, and theslung may be set as slurry for wet molding. Concentration of the slurrymay be performed by centrifugal separation, filter pressing and thelike.

An amount of the fine powder in the slurry for wet molding is preferably30 to 85% by mass. Water or nonaqueous solvent may be used as adispersion medium of the slurry. In addition to water, surfactants suchas gluconic acid, gluconate, and sorbitol may be added to the slurry forwet molding. The molding in a magnetic field is performed by using theslurry for wet molding. A molding pressure is, for example, 0.1 to 0.5ton/cm², and an applied magnetic field is, for example, 5 kOe to 15 kOe.

The firing process is a process of firing the molded body to obtain asintered body. The firing process is typically performed in an oxidizingatmosphere such as in the air. A firing temperature is preferably 1050to 1300° C., and more preferably 1150 to 1250° C. A firing time at thefiring temperature is preferably 0.5 to 3 hours. Through theabove-described processes, it is possible to obtain a sintered body,that is, a sintered ferrite magnet 10. In addition, the method ofmanufacturing the sintered ferrite magnet of the invention is notlimited to the above-described method.

Hereinbefore, a preferred embodiment of the invention has beendescribed, but the sintered ferrite magnet and the motor of theinvention are not limited to the above-described sintered ferrite magnetand motor. For example, the shape of the sintered ferrite magnet is notlimited to the shape in FIG. 1, and may be appropriately modified into ashape that is suitable for the above-described uses.

EXAMPLES

The contents of the invention will be described in more detail withreference to Examples and Comparative Examples, but the invention is notlimited to the following Examples.

Examples 1 to 72, and Comparative Examples 1 to 13 Preparation ofSintered Ferrite Magnet

First, the following starting raw materials were prepared.

Fe₂O₃ powder (primary particle size: 0.3 μm)

SrCO₃ powder (primary particle size: 2 μm)

SiO₂ powder (primary particle size: 0.01 μm)

CaCO₃ powder

Na₂CO₃ powder

K₂CO₃ powder

1000 g of Fe₂O₃ powder, 161.2 g of SrCO₃ powder, and 2.3 g of SiO₂powder were mixed while pulverizing the powders by using a wet attritor,and then drying and granulation were performed. The resultant powderthat was obtained in this manner was fired in the air at 1250° C. for 3hours, thereby obtaining a granular calcined material. The calcinedmaterial was roughly pulverized by using a dry vibration rod mill,thereby preparing a powder having a specific surface area of 1 m²/g inaccordance with a BET method.

Sorbitol, the SiO₂ powder and the CaCO₃ powder were added to 130 g ofroughly pulverized powder in a predetermined amount, and then wetpulverization was performed for 21 hours by using a ball mill to obtainslurry. An added amount of the sorbitol was 1% by mass on the basis ofthe mass of the roughly pulverized powder. The specific surface area ofa fine powder after pulverization was 6 m²/g to 8 m²/g. The Na₂CO₃powder and/or the K₂CO₃ powder were added to the slurry after completionof the pulverization in a predetermined amount, and then stirring wasperformed. Then, a concentration of a solid content of the slurry wasadjusted, and molding was performed by using a wet magnetic fieldmolding machine in an applied magnetic field of 12 kOe, therebyobtaining a molded body. Four pieces of molded bodies were prepared. Themolded bodies were fired in the air at 1180° C., 1200° C., 1220° C., and1240° C., respectively, thereby obtaining four kinds of cylindricalsintered ferrite magnets in which firing temperatures were differentfrom each other. In this manner, sintered ferrite magnets of Example 1were prepared. In addition, sintered ferrite magnets of Examples 2 to 72and Comparative Examples 1 to 13, which had a composition different fromthat of Example 1, were prepared in the same manner as Example 1 exceptthat at least one of an added amount of the SrCO₃ powder beforecalcination, an added amount of the SiO₂ powder and the CaCO₃ powderduring preparation of slurry, and an added amount of the Na₂CO₃ powderand the K₂CO₃ powder to the slurry was changed. In respective Examplesand Comparative Examples, four kinds of sintered ferrite magnets, inwhich firing temperatures were different from each other, were prepared.

(Evaluation of Sintered Ferrite Magnet)

<Composition Analysis>

The composition of the prepared sintered ferrite magnets of respectiveExamples and Comparative Examples was measured by inductively coupledplasma emission spectroscopic analysis (ICP analysis) and fluorescentX-ray analysis. In the sintered ferrite magnets, elements (Ba and thelike), which were derived from impurities contained in the starting rawmaterials, were detected in addition to Fe, Sr, Si, and Ca. Tables 1 to5 show respective amounts of Na, Al, K, Si, Ca, Cr, Mn, Fe, Ni, Sr, andBa which were detected in terms of Na₂O, Al₂O₃, K₂O, SiO₂, CaO, Cr₂O₃,MnO, Fe₂O₃, NiO, SrO, and BaO. Each of the amounts is a value (% bymass) on the basis of the entirety of the sintered ferrite magnet. Inaddition, the reason why the total value of the amounts is not 100% bymass is that each of the sintered ferrite magnets contains a minorcomponent such as an impurity in addition to the above-describedcomponents, and oxidation numbers of constituent elements of respectiveoxides may be different in some cases.

An amount of Sr, which constitutes an A site of the Sr ferrite expressedby General Formula (5), was calculated on the basis of the amount of Fe,Al, Cr, Mn, and Ni on the assumption that Al, Cr, Mn, and Ni, which aredetected by the above-described composition analysis, constitute a Bsite of the Sr ferrite expressed by General Formula (5) in combinationwith Fe. In addition, a rare-earth element R was not contained, and thusx in General Formula (5) is 0. In addition, an amount (% by mass) of Sr(Sr_(F)), which does not constitute the Sr ferrite, was obtained bysubtracting the amount of Sr constituting the A site, which was obtainedas described above, from the amount of Sr that was obtained by theabove-described composition analysis. The amount (% by mass) of Sr,which does not constitute the Sr ferrite, and the amount (% by mass) ofBa, Ca, Na, and K were converted in a molar basis, and a molar ratio a[=(Sr_(F)+Ba+Ca+2Na+2K)/Si] was obtained. These results are shown inTables 1 to 5.

<Evaluation of Magnetic Characteristics>

An upper surface and a lower surface of each of the prepared cylindricalsintered ferrite magnets were processed, and then the magneticcharacteristics were measured by using a B—H tracer in which a maximumapplied magnetic field was 25 kOe. During the measurement, Br, HcJ, bHc,4 PI_(max), and (BH)_(max) were obtained, and an external magnetic fieldintensity (Hk) when reaching 90% of the Br was measured. On the basis ofthe measured values, Hk/HcJ (%) was obtained. In respective Examples andComparative Examples, magnetic characteristics of sintered ferritemagnets, among the sintered ferrite magnets prepared at respectivefiring temperatures of 1180° C., 1200° C., 1220° C., and 1240° C., whichsatisfy a relationship of Hk/HcJ>90% and which shows the highest“Br+1/3HcJ” are shown in Tables 1 to 5 in combination with firingtemperatures.

<Evaluation on External Appearance>

Each of the ferrite magnets that were prepared was left as it was in theair for 7 days, and the surface of the ferrite magnet was observed withthe naked eye. Evaluation was performed on the basis of the followingcriteria. Evaluation results are shown in Tables 1 to 4.

A: Crack did not occur on a surface of a magnet and a white powder wasnot generated thereon.

B: Crack occurred on the surface of the magnet, but the white powder wasnot generated thereon.

C: Crack occurred on the surface of the magnet, and the white powderadhered to the surface.

TABLE 1 Composition Analysis Na₂O Al₂O₃ K₂O SiO₂ CaO Cr₂O₃ MnO Fe₂O₃ NiOSrO BaO mass % mass % mass % mass % mass % mass % mass % mass % mass %mass % mass % Example 1 0.009 0.092 0.001 0.470 0.431 0.077 0.566 87.70.021 10.5 0.058 Example 2 0.044 0.091 0.001 0.432 0.424 0.077 0.56487.7 0.020 10.5 0.052 Example 3 0.081 0.091 0.001 0.433 0.433 0.0770.568 87.7 0.021 10.5 0.054 Example 4 0.007 0.093 0.001 0.498 0.6480.075 0.564 87.5 0.022 10.4 0.057 Example 5 0.013 0.093 0.001 0.4730.641 0.075 0.559 87.6 0.023 10.4 0.059 Example 6 0.051 0.095 0.0010.455 0.646 0.083 0.562 87.5 0.028 10.4 0.054 Example 7 0.086 0.0900.001 0.464 0.648 0.079 0.568 87.4 0.022 10.5 0.059 Example 8 0.0110.089 0.001 0.450 0.209 0.078 0.567 88.0 0.025 10.4 0.056 Example 90.047 0.092 0.001 0.431 0.216 0.078 0.565 88.0 0.020 10.4 0.061 Example10 0.084 0.089 0.001 0.439 0.207 0.079 0.563 87.9 0.022 10.4 0.056Example 11 0.129 0.090 0.001 0.452 0.206 0.074 0.565 87.8 0.021 10.50.058 Example 12 0.135 0.092 0.001 0.451 0.209 0.082 0.565 87.8 0.02310.5 0.058 Example 13 0.004 0.089 0.001 0.740 0.642 0.076 0.556 87.30.025 10.4 0.066 Example 14 0.012 0.093 0.001 0.665 0.643 0.076 0.56187.4 0.022 10.4 0.058 Example 15 0.056 0.090 0.001 0.626 0.640 0.0760.561 87.3 0.021 10.4 0.060 Example 16 0.106 0.090 0.001 0.653 0.6500.079 0.559 87.2 0.021 10.4 0.060 Example 17 0.135 0.095 0.001 0.6640.654 0.079 0.561 87.2 0.022 10.4 0.053 Example 18 0.015 0.092 0.0010.708 0.865 0.075 0.561 87.1 0.021 10.4 0.054 Example 19 0.060 0.0910.001 0.657 0.857 0.074 0.562 87.1 0.020 10.4 0.056 Example 20 0.1000.092 0.001 0.686 0.873 0.075 0.564 87.0 0.022 10.4 0.056 Example 210.012 0.092 0.001 0.696 1.07 0.075 0.560 86.9 0.022 10.4 0.055 Example22 0.049 0.090 0.001 0.665 1.08 0.078 0.560 86.9 0.020 10.4 0.051Example 23 0.094 0.090 0.001 0.671 1.08 0.076 0.557 86.8 0.020 10.40.053 Magnetic Characteristics Molar Firing Br/ Ratio Temp. Br bHc HcJ(BH)_(max) 4PI_(max) Hk/HcJ Br + Appear- a ° C. G Oe Oe MGOe % % ⅓HcJance Example 1 2.25 1220 4139 3603 3859 4.14 96.0 92.2 5.43 A Example 22.74 1200 4128 3756 3902 4.12 96.2 96.3 5.43 A Example 3 3.08 1180 40763740 3974 4.01 95.8 94.9 5.40 A Example 4 2.48 1180 4103 3688 3966 4.0795.9 93.0 5.43 A Example 5 2.63 1180 4099 3577 3778 4.07 96.1 94.0 5.36A Example 6 3.08 1180 4116 3659 3792 4.10 96.2 95.7 5.38 A Example 73.46 1180 4096 3598 3818 4.06 96.0 93.5 5.37 A Example 8 1.66 1220 41843482 3637 4.24 96.7 93.8 5.40 A Example 9 2.08 1220 4158 3555 3711 4.1896.5 94.3 5.40 A Example 10 2.35 1180 4016 3816 4079 3.90 95.8 96.6 5.38A Example 11 2.82 1180 4016 3784 4059 3.90 95.9 95.4 5.37 A Example 122.88 1180 4024 3789 4039 3.92 96.1 96.0 5.37 A Example 13 1.67 1240 41753263 3437 4.19 96.0 92.5 5.32 A Example 14 1.89 1220 4134 3607 3792 4.1295.8 94.4 5.40 A Example 15 2.29 1200 4110 3773 3952 4.07 95.5 96.3 5.43A Example 16 2.51 1200 4111 3772 3964 4.07 95.5 95.9 5.43 A Example 172.64 1180 4071 3768 4043 4.00 95.3 93.9 5.42 A Example 18 2.15 1220 41883508 3703 4.23 95.9 93.3 5.42 A Example 19 2.57 1180 4084 3775 3984 4.0395.7 95.5 5.41 A Example 20 2.72 1200 4141 3594 3803 4.14 95.8 93.4 5.41A Example 21 2.50 1200 4124 3449 3672 4.11 96.2 91.6 5.35 A Example 222.85 1180 4087 3583 3741 4.05 96.1 95.0 5.33 A Example 23 3.10 1200 41793373 3484 4.22 96.4 94.7 5.34 A

TABLE 2 Composition Analysis Na₂O Al₂O₃ K₂O SiO₂ CaO Cr₂O₃ MnO Fe₂O₃ NiOSrO BaO Mass % Mass % Mass % Mass % Mass % Mass % Mass % Mass % Mass %Mass % Mass % Example 24 0.057 0.088 0.001 0.576 0.212 0.077 0.561 87.90.021 10.4 0.051 Example 25 0.097 0.090 0.001 0.591 0.210 0.080 0.56687.7 0.020 10.5 0.056 Example 26 0.140 0.091 0.001 0.613 0.214 0.0810.567 87.6 0.022 10.5 0.059 Example 27 0.050 0.089 0.001 0.602 0.4220.074 0.562 87.6 0.020 10.4 0.058 Example 28 0.114 0.086 0.001 0.6180.437 0.080 0.560 87.5 0.018 10.4 0.053 Example 29 0.135 0.093 0.0010.625 0.433 0.075 0.561 87.4 0.023 10.5 0.063 Example 30 0.068 0.0920.001 0.884 0.867 0.078 0.556 86.9 0.021 10.4 0.057 Example 31 0.1170.090 0.001 0.898 0.871 0.078 0.557 86.8 0.020 10.4 0.057 Example 320.150 0.093 0.001 0.893 0.867 0.073 0.561 86.8 0.015 10.4 0.060 Example33 0.019 0.094 0.001 0.935 1.09 0.074 0.558 86.7 0.021 10.4 0.053Example 34 0.074 0.087 0.001 0.912 1.09 0.073 0.552 86.7 0.019 10.30.062 Example 35 0.069 0.084 0.001 0.910 1.30 0.076 0.552 86.5 0.02110.3 0.063 Example 36 0.113 0.087 0.001 0.912 1.31 0.073 0.556 86.40.021 10.3 0.063 Example 37 0.073 0.093 0.001 0.838 0.428 0.077 0.56387.3 0.021 10.5 0.051 Example 38 0.109 0.091 0.001 0.853 0.438 0.0750.561 87.2 0.021 10.5 0.057 Example 39 0.120 0.095 0.001 0.901 0.6580.070 0.562 87.0 0.020 10.4 0.061 Example 40 0.094 0.090 0.001 0.6040.104 0.080 0.565 87.2 0.0 11.0 0.067 Example 41 0.102 0.088 0.001 0.6070.106 0.073 0.555 86.9 0.0 11.4 0.072 Example 42 0.102 0.088 0.001 0.6190.106 0.073 0.561 86.4 0.0 11.9 0.077 Example 43 0.134 0.094 0.001 0.6520.106 0.076 0.562 86.3 0.0 11.8 0.082 Example 44 0.053 0.089 0.001 0.5950.105 0.079 0.565 87.7 0.0 10.7 0.061 Example 45 0.106 0.090 0.001 0.6070.106 0.073 0.565 87.6 0.0 10.7 0.064 Example 46 0.141 0.098 0.001 0.6240.106 0.077 0.566 87.5 0.0 10.6 0.057 Magnetic Characteristics MolarFiring Br/ Ratio Temp. Br bHc HcJ (BH)_(max) 4PI_(max) Hk/HcJ Br +Appear- a ° C. G Oe Oe MGOe % % ⅓HcJ ance Example 24 1.62 1200 4042 36653864 3.94 95.7 94.8 5.33 A Example 25 1.96 1220 4096 3592 3743 4.05 96.094.8 5.34 A Example 26 2.18 1180 4012 3807 4073 3.89 95.8 97.3 5.37 AExample 27 1.92 1200 4113 3704 3887 4.08 96.0 95.3 5.41 A Example 282.30 1200 4132 3713 3880 4.13 96.1 95.7 5.43 A Example 29 2.51 1180 40833753 3981 4.03 95.9 95.0 5.41 A Example 30 1.97 1200 4028 3729 3989 3.9094.8 94.6 5.36 A Example 31 2.17 1200 4076 3779 4025 4.00 95.2 95.4 5.42A Example 32 2.32 1200 4068 3763 4028 3.98 94.9 94.9 5.41 A Example 331.93 1220 4143 3431 3612 4.14 96.0 92.6 5.35 A Example 34 2.15 1220 41163663 3832 4.08 95.5 94.8 5.39 A Example 35 2.40 1200 4098 3720 3941 4.0595.5 94.4 5.41 A Example 36 2.60 1200 4127 3659 3884 4.11 95.8 93.5 5.42A Example 37 1.58 1220 4093 3504 3659 4.03 95.9 94.6 5.31 A Example 381.74 1200 4064 3633 3764 3.98 95.6 95.7 5.32 A Example 39 1.90 1180 40593771 3982 3.97 95.4 96.3 5.39 A Example 40 2.25 1180 4119 3668 3857 4.0995.6 94.7 5.40 A Example 41 2.71 1220 4065 3668 3819 4.00 95.9 95.6 5.34A Example 42 3.18 1200 4013 3710 3945 3.90 96.0 94.8 5.33 A Example 433.13 1200 3996 3719 4028 3.86 95.7 94.6 5.34 A Example 44 1.67 1220 41023568 3736 4.06 95.9 94.3 5.35 A Example 45 1.99 1220 4077 3622 3807 4.0295.9 94.8 5.35 A Example 46 2.06 1200 4019 3735 3980 3.89 95.5 95.3 5.35A

TABLE 3 Composition Analysis Na₂O Al₂O₃ K₂O SiO₂ CaO Cr₂O₃ MnO Fe₂O₃ NiOSrO BaO Mass % Mass % Mass % Mass % Mass % Mass % Mass % Mass % Mass %Mass % Mass % Example 47 0.154 0.090 0.001 0.685 0.865 0.073 0.556 86.90.0 10.4 0.056 Example 48 0.176 0.088 0.001 0.676 0.873 0.073 0.560 86.90.0 10.4 0.063 Example 49 0.178 0.095 0.001 0.626 0.209 0.081 0.563 87.50.0 10.5 0.059 Example 50 0.202 0.094 0.001 0.892 0.866 0.075 0.553 86.70.0 10.4 0.063 Example 51 0.155 0.091 0.001 0.897 1.08 0.072 0.558 86.50.0 10.4 0.056 Example 52 0.198 0.088 0.001 0.888 1.07 0.073 0.555 86.50.0 10.4 0.050 Example 53 0.159 0.090 0.001 0.908 1.30 0.076 0.560 86.30.0 10.3 0.056 Example 54 0.189 0.092 0.001 0.897 1.31 0.077 0.553 86.30.0 10.4 0.049 Example 55 0.196 0.089 0.001 0.883 0.426 0.074 0.558 87.10.0 10.4 0.050 Example 56 0.201 0.094 0.001 0.885 0.433 0.076 0.564 87.10.0 10.4 0.056 Example 57 0.167 0.095 0.001 0.919 0.652 0.072 0.558 86.90.0 10.4 0.055 Example 58 0.168 0.093 0.001 0.658 0.105 0.078 0.562 87.10.0 11.1 0.064 Example 59 0.307 0.097 0.001 0.678 0.106 0.080 0.560 86.90.0 11.0 0.067 Example 60 0.168 0.093 0.001 0.666 0.107 0.081 0.555 86.70.0 11.4 0.066 Example 61 0.183 0.089 0.001 0.678 0.108 0.078 0.561 86.20.0 11.8 0.080 Example 62 0.175 0.090 0.001 0.647 0.107 0.072 0.560 87.40.0 10.7 0.059 Example 63 0.002 0.121 0.121 0.797 0.952 0.078 0.567 87.50.0 9.7 0.081 Example 64 0.002 0.210 0.210 0.791 0.917 0.075 0.557 87.60.0 9.6 0.083 Magnetic Characteristics Molar Firing Br/ Ratio Temp. BrbHc HcJ (BH)_(max) 4PI_(max) Hk/HcJ Br + Appear- a ° C. G Oe Oe MGOe % %⅓Hc ance Example 47 3.03 1180 4064 3622 3946 3.98 95.6 91.8 5.38 AExample 48 3.21 1180 4074 3585 3881 4.01 95.7 91.7 5.37 A Example 492.37 1200 4035 3740 3930 3.93 95.7 96.3 5.35 A Example 50 2.55 1200 40623772 4034 3.97 95.1 95.0 5.41 A Example 51 2.60 1180 4054 3721 4002 3.9795.3 93.7 5.39 A Example 52 2.80 1180 4040 3707 3973 3.94 95.4 94.0 5.36A Example 53 2.80 1200 4106 3587 3830 4.06 95.5 92.9 5.38 A Example 543.04 1200 4109 3450 3779 4.07 95.8 89.1 5.37 A Example 55 1.98 1220 40733500 3780 3.94 95.7 90.4 5.33 A Example 56 2.01 1200 4053 3734 3923 3.9695.6 96.0 5.36 A Example 57 2.06 1180 4019 3750 4033 3.89 95.2 94.8 5.36A Example 58 2.60 1180 4045 3742 4006 3.94 95.2 94.9 5.38 A Example 593.26 1180 4087 3676 4067 3.95 95.6 90.4 5.44 B Example 60 2.87 1220 40153723 3987 3.89 95.6 95.3 5.34 A Example 61 3.31 1200 3948 3707 4078 3.7795.7 93.8 5.31 B Example 62 2.30 1220 4043 3612 3784 3.95 96.1 95.1 5.30B Example 63 1.84 1220 4079 3584 3852 4.01 95.2 91.8 5.36 A Example 641.97 1200 4023 3638 3925 3.89 95.0 92.7 5.33 A

TABLE 4 Composition Analysis Na₂O Al₂O₃ K₂O SiO₂ CaO Cr₂O₃ MnO Fe₂O₃ NiOSrO BaO mass % mass % mass % mass % mass % mass % mass % mass % mass %mass % mass % Example 65 0.005 0.082 0.001 0.389 0.047 0.072 0.557 88.40.0 10.4 0.057 Example 66 0.004 0.086 0.002 0.320 0.375 0.070 0.561 88.20.0 10.5 0.060 Example 67 0.290 0.089 0.001 0.320 0.200 0.068 0.559 88.30.0 10.4 0.057 Example 68 0.300 0.084 0.002 0.930 1.800 0.072 0.565 86.00.0 10.5 0.057 Example 69 0.300 0.088 0.001 0.935 0.410 0.079 0.559 87.20.0 10.5 0.060 Example 70 0.005 0.080 0.001 0.932 0.690 0.075 0.562 87.20.0 10.5 0.060 Example 71 0.000 0.087 0.010 0.310 0.375 0.077 0.551 88.20.0 10.5 0.060 Example 72 0.001 0.084 0.090 0.464 0.648 0.075 0.558 87.40.0 10.5 0.059 Magnetic Characteristics Molar Firing Br/ Ratio Temp. BrbHc HcJ (BH)_(max) 4PI_(max) Hk/HcJ Br + Appear- a ° C. G Oe Oe MGOe % %⅓HcJ ance Example 65 1.36 1220 4102 3851 3952 4.08 96.1 95.1 5.42 AExample 66 2.97 1220 4162 3551 3652 4.20 96.5 95.6 5.38 A Example 675.63 1200 4168 3561 3659 4.21 96.7 95.9 5.39 A Example 68 4.04 1220 41673329 3451 4.14 96.7 93.8 5.32 A Example 69 2.35 1220 4077 3509 3750 3.9696.2 91.8 5.33 A Example 70 1.45 1220 4067 3529 3751 3.94 96.1 91.8 5.32A Example 71 3.08 1220 4162 3551 3652 4.20 96.5 95.6 5.38 A Example 723.24 1180 4096 3598 3818 4.06 96.0 93.5 5.37 A

TABLE 5 Composition Analysis Na₂O Al₂O₃ K₂O SiO₂ CaO Cr₂O₃ MnO Fe₂O₃ NiOSrO BaO mass % mass % mass % mass % mass % mass % mass % mass % mass %mass % mass % Comp. Ex. 1 0.002 0.093 0.001 0.506 0.853 0.082 0.562 87.30.0 10.4 0.051 Comp. Ex. 2 0.002 0.093 0.001 0.735 0.422 0.075 0.56887.5 0.0 10.4 0.058 Comp. Ex. 3 0.002 0.092 0.001 0.970 0.855 0.0760.561 87.0 0.0 10.3 0.058 Comp. Ex. 4 0.002 0.090 0.001 0.976 1.29 0.0740.552 86.6 0.0 10.3 0.053 Comp. Ex. 5 0.002 0.094 0.001 0.947 0.6470.077 0.559 87.1 0.0 10.4 0.052 Comp. Ex. 6 0.002 0.093 0.001 0.7370.105 0.081 0.554 87.3 0.0 11.0 0.064 Comp. Ex. 7 0.002 0.091 0.0010.736 0.106 0.080 0.558 86.8 0.0 11.4 0.067 Comp. Ex. 8 0.002 0.0900.001 0.730 0.106 0.075 0.559 86.5 0.0 11.8 0.074 Comp. Ex. 9 0.0020.091 0.001 0.724 0.106 0.079 0.556 86.1 0.0 12.2 0.078 Comp. Ex. 100.002 0.091 0.001 0.600 0.102 0.074 0.557 86.7 0.0 11.7 0.083 Comp. Ex.11 0.002 0.091 0.001 0.849 0.866 0.082 0.563 87.1 0.0 10.3 0.083 Comp.Ex. 12 0.002 0.085 0.001 0.274 0.098 0.075 0.559 88.2 0.0 10.5 0.060Comp. Ex. 13 0.002 0.088 0.001 0.274 0.098 0.077 0.561 88.3 0.0 10.50.058 Magnetic Characteristics Molar Filing Br/ Ratio Temp. Br bHc HcJ(BH)_(max) 4PI_(max) Hk/HcJ Br + Appear- a ° C. G Oe Oe MGOe % % ⅓HcJance Comp. Ex. 1 2.85 1180 4140 2524 2719 4.14 96.1 86.1 5.05 A Comp.Ex. 2 1.32 1220 4094 3101 3275 3.99 95.9 90.2 5.19 A Comp. Ex. 3 1.451220 4119 3223 3354 4.09 95.6 93.6 5.24 A Comp. Ex. 4 1.95 1220 41143279 3540 4.08 95.5 90.1 5.29 A Comp. Ex. 5 1.30 1220 4067 3029 31513.94 96.1 91.8 5.12 A Comp. Ex. 6 1.35 1180 4210 2742 2877 4.28 96.590.1 5.17 A Comp. Ex. 7 1.71 1180 4181 2634 2741 4.23 96.4 92.6 5.0 AComp. Ex. 8 2.07 1180 4099 3247 3386 4.06 96.6 93.4 5.23 A Comp. Ex. 92.45 1200 3934 2869 2946 3.76 96.3 93.0 4.92 A Comp. Ex. 10 2.41 12204107 2798 2932 4.09 96.8 90.6 5.08 A Comp. Ex. 11 1.68 1220 4146 31123265 4.14 95.2 92.4 5.23 A Comp. Ex. 12 2.34 1220 4041 2200 2266 3.9396.8 91.6 4.80 A Comp. Ex. 13 2.32 1220 4218 1818 1842 3.97 97.3 91.94.83 A

As shown in Tables 1 to 5, in the sintered ferrite magnets of Examples,the crack did not occur and the white powder was not generated, and avalue of the “Br+⅓HcJ” was 5.3 or more. In addition, in a sinteredferrite magnet in which the total amount of Na and K in terms of Na₂Oand K₂O was more than 0.31% by mass, it was confirmed that a cracktended to occur, and when the sintered ferrite magnet was left as is inthe air for a predetermined period of time, the white powderprecipitated in some cases. In addition, when a ratio of the molar ratioa was too large or too small, a phenomenon in which the magneticcharacteristics decreased or the reliability deteriorated was confirmed.

Examples 73 and 74, and Comparative Example 14 Preparation of SinteredFerrite Magnet and Evaluation Thereof

The same starting raw materials as Example 1 were prepared. 1000 g ofFe₂CO₃ powder, 161.2 g of SrCO₃ powder, and 2.3 g of SiO₂ powder weremixed while pulverizing the powders by using a wet attritor, and thendrying and granulation were performed. The resultant powder that wasobtained in this manner was fired in the air at 1250° C. for 3 hours,thereby obtaining a granular calcined material. The calcined materialwas roughly pulverized by using a dry vibration rod mill, therebypreparing a powder having a specific surface area of 1 m²/g inaccordance with a BET method.

Sorbitol, the SiO₂ powder and the CaCO₃ powder were added to 200 g ofroughly pulverized powder in a predetermined amount, and then wetpulverization was performed for 40 hours by using a ball mill to obtainslurry. An added amount of the sorbitol was 1% by mass on the basis ofthe mass of the roughly pulverized powder. The specific surface area ofa fine powder contained in the slurry was 6 m²/g to 8 m²/g. The Na₂CO₃powder and/or the K₂CO₃ powder were added to the slurry after completionof the pulverization in a predetermined amount, and then stirring wasperformed. Then, a concentration of a solid content of the slurry wasadjusted, and molding was performed by using a wet magnetic fieldmolding machine in an applied magnetic field of 12 kOe, therebyobtaining a molded body. The molded body was fired in the air at 1180°C. to 1240° C., thereby obtaining a cylindrical sintered ferrite magnet.In this manner, sintered ferrite magnets of Examples of 73 and 74 andComparative Example 14 were prepared. Evaluation on the preparedsintered ferrite magnets was performed in the same manner as Example 1.Results thereof are shown in Table 6.

TABLE 6 Composition Analysis Na₂O Al₂O₃ K₂O SiO₂ CaO Cr₂O₃ MnO Fe₂O₃ NiOSrO BaO Mass % Mass % Mass % Mass % Mass % Mass % Mass % Mass % Mass %Mass % Mass % Example 73 0.044 0.057 0.001 0.727 0.859 0.088 0.561 87.20.027 10.3 0.074 Example 74 0.105 0.053 0.001 0.736 0.873 0.086 0.55887.1 0.028 10.3 0.067 Comp. Ex. 14 0.002 0.051 0.001 0.849 0.866 0.0820.563 87.1 0.030 10.3 0.083 Magnetic Characteristics Molar Firing Br/Ratio Temp. Br bHc HcJ (BH)_(max) 4PI_(max) Hk/HcJ Br + Appear- a ° C. GOe Oe MGOe % % ⅓HcJ ance Example 73 2.26 1200 4136 3605 3779 4.12 95.193.8 5.40 A Example 74 2.74 1200 4122 3597 3854 4.09 95.1 92.6 5.41 AComp. Ex. 14 1.67 1200 4113 3126 3312 4.08 95.2 91.1 5.22 A

A cross-section (a plane) of each of the sintered ferrite magnets ofExamples 73 and 74 and Comparative Example 14 was mirror-polished, andthen the cross-section was etched with a hydrofluoric acid. Then, theresultant etched surface was observed with an FE-SEM. FIG. 3 is anelectron microscope photograph illustrating an enlarged cross-section ofthe sintered ferrite magnet of Example 73 (magnification: 10,000 times).FIG. 4 is an electron microscope photograph illustrating an enlargedcross-section of the sintered ferrite magnet of Example 74(magnification: 10,000 times). FIG. 5 is an electron microscopephotograph illustrating an enlarged cross-section of the sinteredferrite magnet of Comparative Example 14 (magnification: 10,000 times).

It was confirmed that in the sintered ferrite magnets shown in FIGS. 3and 4, a deviation in a grain size of crystal grains of the Sr ferritewas smaller and the maximum grain size of crystal grains of the Srferrite was smaller in comparison to the sintered ferrite magnet shownin FIG. 5. In the images shown in FIGS. 3 to 5, a contour of crystalgrains of the Sr ferrite was made to be clear. Then, a grain sizedistribution of crystal grains of the Sr ferrite on the number basis wasmeasured by image processing.

FIG. 6 is a histogram illustrating a grain size distribution of crystalgrains of the Sr ferrite that is contained in the sintered ferritemagnet of Example 73. FIG. 7 is a histogram illustrating a grain sizedistribution of crystal grains of the Sr ferrite that is contained inthe sintered ferrite magnet of Example 74. FIG. 8 is a histogramillustrating a grain size distribution of crystal grains of the Srferrite that is contained in the sintered ferrite magnet of ComparativeExample 14.

From grain size distribution data, an average grain size of crystalgrains of the Sr ferrite on the number basis and a standard deviationthereof were obtained. In addition, an aspect ratio of each of thecrystal grains was measured, and an average value of the aspect ratio onthe number basis and a standard deviation thereof were obtained. Resultsthereof are shown in Table 7. In Examples 73 and 74, a ratio of crystalgrains having a grain size of 2.0 μm or more to the entirety of crystalgrains of the Sr ferrite on the number basis was 1% or less. Incontrast, in Comparative Example 14, a ratio of crystal grains having agrain size of 2.0 μm or more to the entirety of crystal grains of the Srferrite on the number basis exceeded 1%.

With respect to the sintered ferrite magnets that were obtained inExamples 1 to 5, etching was performed in the same manner as Example 73,and then observation with the FE-SEM was performed. After a contour ofcrystal grains of the Sr ferrite was made to be clear in imageprocessing as shown in FIGS. 3 to 5, a grain size distribution ofcrystal grains of the Sr ferrite on the number basis was measured byimage processing. From grain size distribution data, the average grainsize of crystal grains of the Sr ferrite on the number basis and thestandard deviation thereof were obtained. In addition, an aspect ratioof each of the crystal grains was measured, and an average value of theaspect ratio on the number basis and a standard deviation thereof wereobtained. Results thereof are shown in Table 7. Even in the sinteredmagnets of Examples 1 and 5, a ratio of crystal grains having a grainsize of 2.0 μm or more to the entirety of crystal grains of the Srferrite was 1% or less.

TABLE 7 Grain Size (μm) Aspect Ratio Example 73 Average Value 0.80 1.60Standard deviation 0.42 0.46 Example 74 Average Value 0.79 1.54 Standarddeviation 0.40 0.38 Example 1 Average Value 0.79 1.50 Standard deviation0.38 0.36 Example 5 Average Value 0.82 1.48 Standard deviation 0.41 0.42Comparative Average Value 0.85 1.62 Example14 Standard deviation 0.430.48

Even in the sintered ferrite magnets of other Examples, the grain sizedistribution of the Sr ferrite was measured in the same manner asExample 1, and the average grain size of crystal grains of the Srferrite on the number basis and the standard deviation thereof wereobtained. As a result, in all of the sintered ferrite magnets ofExamples, the average grain size of crystal grains of the Sr ferrite was1.0 μm or less. In addition, in all of the sintered ferrite magnets ofExamples, a ratio of crystal grains having a grain size of 2.0 μM ormore to the entirety of crystal grains of the Sr ferrite on the numberbasis was 1% or less.

<Composition Analysis 2>

A composition inside crystal grains of ferrite constituting the sinteredbody of Example 74, and a composition in the vicinity of a grainboundary between two crystal grains were measured by using ahigh-resolution TEM-EDS. At the inside of crystal grains and in thevicinity of the grain boundary, a spectrum was 100-point measured, andthe resultant values were integrated and quantified. This measurementwas performed for five sites at the inside of crystal grains and in thevicinity of the grain boundary, respectively. When the total amount ofNa, Si, Ca, Fe, and Sr was set to 100% by mass, an amount of eachelement is shown in Table 8. In addition, it is difficult to measure thecomposition at the grain boundary alone, and thus a measured value inthe vicinity of the grain boundary is affected by the composition insidegrains.

TABLE 8 Measure- ment Na Si Ca Fe Sr Point mass % mass % mass % mass %mass % In the 1 6.7 8.5 1.4 80.8 2.7 vicinity 2 7.3 8.4 1.1 80.4 2.8 ofgrain 3 7.6 8.5 1.5 79.8 2.7 boundary 4 7.3 13.2 3.6 72.8 3.2 5 4.6 7.21.5 83.6 3.1 Inside of 1 1.1 5.1 0.7 90.0 3.2 crystal 2 1.7 5.0 0.2 90.13.0 grains 3 1.4 5.4 0.8 89.0 3.4 4 0.9 5.3 0.3 90.4 3.2 5 0.9 5.3 0.390.2 3.3

As shown in FIG. 8, it was confirmed that similar to Si and Ca, Na wasalso present at the grain boundary portion with a higher concentrationin comparison to the inside of crystal grains.

INDUSTRIAL APPLICABILITY

According to the invention, it is possible to provide a sintered ferritemagnet which is excellent in both characteristics of Br and HO and whichhas high reliability. In addition, it is possible to provide a motorwhich has high efficiency and is excellent in reliability.

REFERENCE SIGNS LIST

-   -   10: Sintered ferrite magnet

The invention claimed is:
 1. A sintered ferrite magnet, comprising:M-type Sr ferrite having a hexagonal crystal structure, wherein a totalamount of Na and K is 0.004 to 0.169% by mass in terms of Na₂O and K₂O,an amount of Si is 0.3 to 0.94% by mass in terms of SiO₂, and thefollowing Expression (1) is satisfied:1.3(Sr_(F)+Ba+Ca+2Na+2K)/Si≦5.7  (1), wherein in Expression (1), Sr_(F)represents an amount of Sr, on a molar basis, other than Sr whichconstitutes the Sr ferrite, and Ba, Ca, Na, and K represent amounts ofrespective elements on a molar basis, wherein the following Expression(3) is satisfied:Br+1/3HcJ≧5.3  (3), wherein in Expression (3), Br and HcJ represent aresidual magnetic flux density (kG) and a coercive force (kOe),respectively.
 2. A sintered ferrite magnet, comprising: M-type Srferrite having a hexagonal crystal structure, wherein a total amount ofNa and K is 0.004 to 0.169% by mass in terms of Na₂O and K₂O, an amountof Si is 0.3 to 0.94% by mass in terms of SiO₂, and the followingExpression (1) is satisfied:1.3≦(Sr_(F)+Ba+Ca+2Na+2K)/Si≦5.7  (1), wherein in Expression (1), Sr_(F)represents an amount of Sr, on a molar basis, other than Sr whichconstitutes the Sr ferrite, and Ba, Ca, Na, and K represent amounts ofrespective elements on a molar basis, wherein an average grain size ofcrystal grains of the Sr ferrite is 1.0 μm or less, and a ratio of thecrystal grains, which have a grain size of 2.0 μm or more, on the numberbasis is 1% or less.
 3. A motor, comprising: the sintered ferrite magnetaccording to claim
 1. 4. A motor, comprising: the sintered ferritemagnet according to claim 2.